What Could Have Been: Leonardo DiCaprio was originally going to voice Jack Frost, but he dropped out supposedly because of schedule conflicts. His voice is somewhat higher and would've fit Jack's apparent age more than Chris Pine's. (Leonardo had previously played a character named Jack as well.)note Which would have been one hell of an Actor Allusion as both versions of Jack involve death by drowning in freezing cold water!
Early casting reports also reported Christopher Lee as a choice for the voice of North.
This is why Bunnymund is such a different character- he was going to be closer to the books until they brought Hugh Jackman in as his voice; which is where he then immediately became the warrior type he is in the movie.
Guillermo Del Toro's suggestion for the story was to have Jamie be the Audience Surrogate. And at least one early version had the climax take a darker turn in which Pitch uses his Nightmare Galleon to harpoon the Moon to create an eclipse to gather his dark forces under for an assault against the Man in the Moon himself.
And as shown in the Art Book of Rise of the Guardians there are several illistrations of Sandy's Sandship, which flies around the world constantly remaining within the twilight time zone region to help Sandy spread dreams. The ship took many forms all revolving around an ocean theme with the ship even resembling a turtle and whale at one point. The ship was to be included in battle against Pitch, where the Nightmares overpowering the ship and eventually consuming it, with Jack reaching out for Sandy's hand before he fades as well.
Some more early concept art for the film reveals that initial designs for Pitch were much more demonic and nightmarish than the film's version of him, which isn't all that different from the books. The concept art also reveals a scene in which Pitch joins with his nightmare sand and becomes as tall as a skyscraper, raining nightmares down upon the world, with Jack clinging on for dear life and looking down at the nightmare sand entering peoples' homes.
There was almost a Jack Frost doll made by Mattel.
Translation error: In the German synchronisation, Bunny is not afraid of the Groundhog beeing chosen as a new Guardian, but of it beeing the "Butzemann". This is not only odd, but outright wrong, since the Butzemann is a synonym of "Der schwarze Mann", which is the Bugeyman...